Reverberation unit



July 2, 1968 G. s. KLAIBER ETAL REVERBERATION UNIT 2 Sheets-Sheet 1Filed Dec. 21, 1964 (lfgpa m4 flan did R 05 mm F L RP m EM M a A K J/ wu 1 E 0 c L MM m5 R R an a5 MW MN VA 5 m L y 1968 G. s. KLAIBER ETAL 3,

REVERBERATION UNIT Filed Dec. 21 1964 2 Sheets-Sheet 2 United StatesPatent 3,391,250 REVERBERATION UNIT George Stanley Klaiber, Tonawanda,and Anthony C.

Ippolito, North Tonawanda, N.Y., assignors to The Wurlitzer Company,Chicago, 11]., a corporation of Ohio Filed Dec. 21, 1964, Ser. No.419,730 11 Claims. (Cl. 179-1) ABSTRACT OF THE DISCLOSURE Areverberation unit for electrical musical instruments and the likeutilizing a helica'ly coiled spring as a signal time-delay element,combined with dampers on transducers at either end thereof to producesatisfactory results with but a single spring.

This invention relates to apparatus for producing timedelay orreverberation effects in musical instruments, phonographs, taperecorders and the like.

It has been recognized heretofore that one defect of home reproductionof music is that the music is generally reproduced or produced in a roomwhich is substantially smal'er than is desirable for proper acousticeffects. It will be recognized that the reverberation time of a largeconcert hall is inherently much greater than that of a domestic livingroom. Various attempts have been made to produce reverberationsynthetically in order to simulate a large concert hall. Probably themost successful artificial or synthetic reverberation devices haveutilized eectromechanical devices for delaying a signal, preferablyintroducing echoes therein. It has been recognized heretofore that thiscan be done by way of one or more springs having motion imparted theretoat one end in accordance with an electrical signal and having anelectrical signal derived at the opposite end from the mechanicalmovement of the spring.

The production of delayed sound transmission by imparting vibrations toone end of a spring is well known. The spring may vibrate in a torsion,compression or transverse mode alternatively, as taught in Wegel US.Patent 1,852,795. Such spring time-delay systems have also been usedspecifically in the musical arts, see for exampe Hammond US. Patent2,230,836 and Meinema U.S. Patent 2,982,819.

It is recognized that any spring inherently has its own natural periodof vibration. Obviously, if the spring tends to resonate at an audiofrequency which is to be delayed in time to produce a reverberationeffect, this frequency will be emphasized. In any event, the motionimparted to a spring electromechanically will travel back and forththrough the spring with a plurality of echoes, as is essential tosimulate concert hall reverberation wherein there are many echoes. Someof the echoes or reflected waves will be in phase with one another andproduce an augmented result. On the other hand, some of the reflectionsor echoes, will be out of phase and will cancel one another. As aresult, there is not a smooth frequency curve, but rather a curve havingalternate peaks and valleys wherein the reflected and direct signalsreinforce and cancel one another. I

Due to this cancellation effect and the peaks and valleys of theresponse curve, it heretofore has been thought essential to have two ormore strings of different natural periods of vibration. It has beenassumed that the peaks of one spring will fill in the valleys of theother, and vice versa. Unfortunately, it has been found that althoughthis does sometimes happen, there are also reinforcement andcancellation effects of the peaks and valleys of the two springs. Italso has been thought essential to have a rather limply suspended springso that it will not tend to resonate at an audio frequency in which itis desired to develop reverberation. This has necessitated the provisionof rather large gaps in the transducers at either end of the spring toavoid bumping together of parts of the transducers upon movement of thesprings other than compressionally or torsionally. This, in turn, hasled to low efliciency of transducing. Limp suspension has alsonecessitated various provisions to prevent the spring from swingingaround upon any physical shocks being imparted to the reverberationapparatus. Bumping together of adjacent coils of the spring, bumping ofparts of the transducer, or bumping of the spring against the framecause extremely unpleasant percussive sounds in the output.

It is an object of the present invention to provide an artificialreverberation system utilizing but a single helical spring.

It is a further object of this invention to provide an artificialreverberation apparatus of greater efliciency than those heretoforeknown in the art.

Yet another object of the invention is to produce an artificialreverberation apparatus having extended frequency response.

Other and further objects and advantages of the present invention willbe apparent from the following description when taken in connection withthe accompanying drawings wherein:

FIG. 1 is a block diagram illustrating a system utilizing thereverberation apparatus of the present invention;

FIG. 2 is a perspective view of a reverberation apparatus constructed inaccordance with the present invention;

FIG. 3 is a longitudinal sectional view through the apparatus of FIG. 2as taken along the line 3-3 in FIG. 2, FIG. 3 being on a larger scaleand with the center portion broken away to foreshorten the figure;

FIG. 4 is an end view of an insulating form or support forming a part ofthe reverberation apparatus;

FIG. 5 is a cross sectional view on the same scale as FIG. 3 and takenalong the line 55 in FIG. 8;

FIG. 6 is a cross sectional view taken along the line 66 in FIG. 8;

FIG. 7 is a detail view of the attachment of the spring to the springanchor taken in longitudinal section and on an enlarged scale;

FIG. 8 is a fragmen ary longitudinal. sectional view taken along theline 8-8 in FIG. 3 and on a larger scale;

FIG. 9 is an exploded perspective view of one of the transducers andadjacent parts; and

FIG. 10 is a sectional view along the line 1010 in FIG. 6.

Circuits utilizing artificial reverberation apparatus are known, and onesuch circuit is shown in FIG. 1. Thus, there is an electrical tonesource providing electric oscillations corresponding to a tone which isto have reverberation thereto. This may be, for example, the tonegenerators of an electronic organ. Alternatively, it can be the pickupof a phonograph, or tape recorder, or a signal source in a radio. Theelectric signal from the tone source 20 is fed to an amplifier 22, andthrough a resistor 24 to a loudspeaker 26. In addition, the output fromthe amplifier is taken by means such as a wire 28 to the reverberationapparatus 30 which in turn is connected to a reverberation amplifier 32.This amplifier is shown as being connected to the loudspeaker 26,although it is known that it could be connected to a separateloudspeaker.

Referring now to FIGS. 2 and 3, there will be seen a reverberationapparatus 3t] constructed in accordance with the principles of thisinvention, and including a channelshaped frame 34 having a relativelywide and elongated web 36 with longitudinal flanges 38 along the edgesthereof. At the ends of the flanges are holes 40 for receipt ofdiagonally tensioned springs 42 to suspend the reverberation apparatussubstantially free of external vibrations. Relatively adjacent the endsof the flanges 38 there are provided somewhat larger semicircularopenings 44. Intermediate the openings 44 the edges of the flanges areturned out at an acute angle to form longitudinal lips 46. These lipsprovide additional rigidity and inhibit any resonance of the frame.

Adjacent the left end of the frame 34 there is disposed a transducingunit or transducer 48, for clarity of nomenclature hereafter referred toas a sending transducer. An identical transducer or transducing unit 48ais secured to the frame near the right end thereof, and this transducerwill for the sake of distinction be referred to as a receiv ingtransducer. It will be understood that electrical energy could be fedinto either of the transducers 48, 48a and taken from the other.

A helically coiled elongated spring 50 is tensionally supported betweenthe two transducers, extending substantially from end to end of theframe. This spring normally is wound with initial tension so that theadjacent convolutions initially are in contact with one another. Thespring is stretched somewhat during installation so that the adjacentcoils or convolutions are pulled apart. This provides for a uniform, butclose spacing between adjacent turns. The spacing is sufliciently smallthat it is diflicult to show it in the scale of FIG. 3. However, it willbe seen in FIG. 8.

As has been noted, the two transducers 48 and 48a are identical. Hence,attention will now be directed to the left or sending transducer 48 forthe details thereof. The transducer 48 is mounted by means of a stud 52staked at 54 in a hole provided therefor in the web 36 of the channel34. The stud is provided at its other end with a tapped axial borereceiving a screw 56 which holds down a U-shaped cover plate 58 having aweb 60 and a pair of side flanges 62. Also held by the screw 56 andbeneath the cover 58 is a U-shaped bracket 64 of relatively heaviermaterial. Although the cover 58 may conveniently be formed of sheetsteel, the bracket 64 is made of brass or other nonmagnetizablematerial. The bracket includes a web 66 and side flanges or legs 68having extending tongues 70 at the ends thereof received in transverseslots 72 in the web 36 of the supporting frame 34 for proper positioningof the frame or bracket 64. Other details of the frame or bracket 64will be set forth hereinafter. It will be observed that the cover 58 isrotated 90 from the position of the bracket 64, whereby the flanges 62of the cover fill in the space between the flanges 68 of the bracket.

The transducer further includes an insulating mounting block or base 74,preferably molded of plastic material. On the front face of the block,which is of generally square outline (the side viewed in FIG. 4 and onthe right in FIGS. 3 and 8-10), the block is recessed at 76, leaving aperipheral wall 78. A magnetic structure 80 of open rectangular outlineis received in this recess within the wall 78. The magnetic structure ismade of magnetically susceptible material, but is not permanentlymagnetized. It is of an open square shape with a pair of confrontinginward protrusions 82 having screw holes 84 therethrough. There aremating screw holes 86 in the plastic block extending completelytherethrough. The magnetic structure 80 is permanently retained in theplastic block, as by means of a suitable adhesive.

The block further is recessed on the front face at 88 to accommodate acoil 90 wound on a magnetically susceptible core 92, and having plasticend pieces 94 and leads 96. As will be seen particularly in FIG. 9, thecore 92 has a small cylindrical protrusion 98 on its upper end. Theplastic end piece 94 has a central square opening complementary in shapeto the core, and the cylindrical protrusion 98 is recessed slightlybelow the upper surface of the plastic end piece 94.

The back side of the plastic block 74 (see particularly FIG. 5) isprovided with a generally V-shaped cut out 100 extending through theblock into communication with the recess 88. Parallel legs 102 form anupward extension of the cut out. The leads 96 from the coil extend intothe V-shaped cut out and up the extensions 102 past edge flanges 104 onthe back side of the block. The coil 90 and associated parts arepermanently held in the recess in the front face of the block, as by asuitable adhesive.

Screws 106 pass through the screw holes 84 in the magnetic structure,through the screws 86 in the block, and threaded into tapped apertures108 in the adjacent leg or flange 68 of the bracket 64 to mount theblock thereon.

The back or outer flange 68 of the bracket 64 is provided with a pair ofears 110 struck out at right angles thereto. The cars are coplanar,being relatively toward adjacent sides of the flange, and are providedat their outer ends with V-shaped notches 112. A beryllium copper Wire114 is bent over the upper ear 110, through the V-shaped notch thereof,and is held in place by a lump of solder 116. The opposite flange 68 isprovided with bores 118 substantially aligned with the surfaces of theears 110 disposed opposite the frame or mounting channel 34. Theberyllium copper wire 114, which serves as an anchor or torsion wire, aswill be brought out hereinafter, is mounted on only one of the ears 112and extends through the corresponding aperture or bore 118. Moreimportantly, the wire extends through a damper or damping member 120made of rubber or other suitable elastomeric material of particularcharacteristics and suiting a particular purpose, as hereinafter broughtout.

The rubber damper 120 of generally cylindrical nature is provided withan axial pin hole substantially less in diameter than the wire 114, andthe wire extends therethrough. The substantially cylindrical damper isprovided near one end, the left end as viewed in FIG. 8 with acircumferential, radially outwardly extending flange 122. This providesa cylindrical protrusion 124 at the left end which extends into the hole118 in the flange 68, being held therein by a suitable adhesive with theflange 122 abutting the face of the flange. There is a longercylindrical protuberance 126 at the opposite end, and this extends intoa bore 128 in the plastic mounting block 74. The bore or pin holethrough which the wire 114 extends in the plug 120 is identified by thenumeral 130, and this bore flares outwardly at 132 at either end.

Within the plastic block 74 and extending therefrom a stainless steeltube 134 (see particularly FIG. 7) is crimped onto the wire 114, and isbent into a hook shape at 136, the adjacent end of the spring 50 havinga hook 138 interen-gaging therewith. The end of the steel tube is spaced.015 inch from the end of the rubber damper 120, the wire being .007inch diameter. In addition, there is disposed on the stainless steeltube a ceramic magnet 140 of cylindrical configuration, being .062 inchoutside diameter, and of substantially the same length as the transversedimension of the core 92, the ceramic magnet being aligned with the endof the core 92, and particularly the protuberance 198 thereof. Theceramic magnet 140 is polarized diametrically, rather than axially, andthis polarization is ideally in a plane perpendicular to the core 92,i.e., parallel to the plane of the adjacent face of the core. It will beobserved particularly in FIG. 8 that the ceramic magnet 140 iscentralized bet-ween the confronting face of the core 92 and theadjacent portion of the square magnetic structure 80.

Thus, when the coil 90 is energized with audio frequency, electricalenergy, it imposes a twisting or torsional force on the magnet 140.This, in turn, excites the reverberation spring 50 in a torsional mode.A signal corresponding to that applied to the coil 90 travels down thespring 50 to twist the ceramic magnet 140a at the opposite end thereof,and thereby to induce a signal in the coil 90a of similar nature, butdelayed in time. As will be appreciated, not all of the energy impartedto the spring is taken up in inducing an electric current in the coil90a. Part of the energy is reflected at the point where the spring ishooked on to the magnet 140a and associated structure, travels back tothe sending end, and again is reflected to the receiving end. There willbe a rather large number of such echoes, andthis results in a receivedsignal remarkably similar to that in a reverberative concert hall orauditorium.

Several details of construction of the present invention, heretoforedescribed, are worthy of amplification. Thus, it will be observed thatthe structure of the transducers is symmetric. There are two ears 110,two holes 118, and two bores 128, even though there is only one springand anchoring structure including wire 114, etc. With this symmetricalconstruction, exactly the same parts can be used at either end. Thus,only one part need be formed instead of two, thereby materially reducingthe cost of dies, inventory, etc.

The spring 50 is made of music wire. Springs of beryllium copper,Phosphor bronze, tempered silver, and stainless steel have been found towork satisfactorily under some circumstances, but the music wire worksbest. The wire itself is of .014 inch diameter, and the spring is woundon a helix so that the spring has an outside diameter of inch. Thespring is wound with initial tension so that the adjacent turns orconvolutions initially abut one another. The initial spring length is 9%inches, and the spring in installed position is stretched to 13 inchesand is under 8 /2 ounces tension. The spring has a natural frequency ofabout 9 cycles per second. Peaks and valleys in transmission areproduced about every 13 cycles on the spring.

Transmission efficiency is increased with increasing axial tension onthe spring. However, there is a tendency to produce chattering withundue tension on the spring. Furthermore, with increased tensionproducing increased efficiency, there is a tendency for a burst ofenergy imparted on the spring to travel up and down the springsubstantially indefinitely, and thereby masking a subsequent note beingplayed. The problems of chattering and of practically infinite hangingon of reflected energy are concurrently solved by the rubber dampers120. These dampers are made of butyl rubber, and preferably are of 40durorneter hardness. Dampers with durorneter readings of 40, 50, 60, 70and 80 all have been satisfactory, but a 40 durorneter reading is best.The position of the damper is quite important, and this is as close aspossible to the magnet and stainless steel tube, or stated otherwise, itis as far as possible away from the point of attachment of the torsionalanchoring wire 114. The damping is four or five times greater than hasbeen used heretofore with two spring units. Nevertheless, since theinitial efficiency is so much higher, the output is still enough higherthat a stage of amplification can be omitted.

By and large, the single spring unit sounds better than previous twospring reverberation units, partially due to lack of cancellationeffects inherent in the use of two springs, and also due to longerhanging on of the reverberation effect due to the higher efliciency andgreater output in the first place.

Many prior helical spring type reverberation units have been quiterestricted in frequency response. Some of these have been found to haveno significant output much above 3,000 cycles per second, and at leastone unit has been found to cut off above 2,800 cycles per second. Areverberation unit constructed in accordance with the principles of thepresent invention has been found to have very good response up to 6,000or 7,000 cycles per second. Propagation of energy through a helicalspring as in the present invention is at the same rate as if it werethrough a straight wire equal to the length of the spring uncoiled.Thus, it will be appreciated that the same results could be obtained ina shorter length by using a coil of greater diameter. However, thepresent dimensions have been found to be optimum. Increasing thediameter of the coil results in there being less coils for a given wavelength of a higher note, such for example on the order of 5,000 cyclesper second. If, for example, there were only about two coils to a wavelength, instead of about six as in the present invention, then therewould be a tendency for the wire itself to twist, instead of justtwisting of the spring, with resultant undesired damping out ofvibrations.

It will be understood that the particular example of the invention asshown and described herein is set forth by way of illustration. Variouschanges in structure will no doubt occur to those skilled in the art,and will be understood as forming a part of the present inventioninsofar as they fall within the spirit and scope of the appended claims.

We claim:

1. A reverberation unit comprising a supporting base; a pair ofelectromagnetic transducers mounted on said base in spaced apartrelation; and a helical spring stretched between said transducers; eachof said transducers including an insulating base, means supporting eachinsulating base from said supporting base, a coil mounted centrally ofeach insulating base, a core in each coil, a surrounding magneticstructure on each insulating base substantially symmetrically disposedabout said coil, there being an air gap at each end of said core betweensaid core and said magnetic structure, a pair of apertures through saidinsulating base respectively aligned with said air gaps and a pair ofanchor means supported from said supporting base and respectivelyaligned with said apertures, a single torsion wire anchored to only oneof the anchor means of each transducer and passing through thecorresponding aperture in said insulating base, means mounting apermanent magnet on said torsion wire in only one of said air gaps ofeach transducer, means joining said spring at its opposite ends to saidtorsion wires; en ergization of the coil of one transducer with an audiofrequency electric signal imparting a twisting motion to thecorresponding permanent magnet and torsionally exciting said helicalspring, said spring in turn imparting a twisting movement to thepermanent magnet of the other transducer and inducing in the coil ofsaid other transducer an audio frequency signal similar to theenergizing frequency but delayed in time therefrom, and a damper ofelastomeric material mounted in the aperture in said insulating basethrough which said torsion wire passes and engaging said torsion wire.

2. A reverberation unit comprising a supporting base, a pair ofelectromagnetic transducers mounted on said base in spaced apartrelation, and a. helical spring stretched between said transducers, eachof said transducers including a base, an elongated torsion wire suportedat one end from each transducer base, a magnetic member mounted on saidtorsion wire and free to move therewith, complementary electromagneticstructure mounted on each insulating base in proximity to the magneticmember on the torsion wire, an elastomeric damper mounted from eachinsulating base in damping engagement with the respective torsion wireand having a hardness between substantially 40 and durorneter, and meansinterconnecting each torsional wire and the adjacent end of said helicalspring.

3. A reverberation unit comprising a supporting base, a pair ofelectromagnetic transducers mounted on said base in spaced apartrelation, and a helical spring stretched between said transducers, eachof said transducers including a base mounted on said supporting base, anelongated torsion wire secured at one end thereof to each of saidtransducer bases and secured at the other end to the respective ends ofsaid spring, a magnetic member secured to each of said torsion Wiresadjacent the end thereof secured to said spring, magnetic structureincluding a coil carried by each of said transducer bases in proximityto the respective magnetic members, and a damper acting on each torsionwire, each of said dampers comprising an elastomeric member supportedfrom the respective transducer base with said wire passing through andin intimate contact with said elastomeric member, said elastomericmembers being disposed immediately adjacent said magnetic members.

4. A reverberation unit as set forth in claim 3 wherein each of saidmagnetic members comprises a cylindrical permanent magnet having apredetermined length, and wherein the spacing between each damper andthe adjacent magnetic member is less than said predetermined length.

5. A reverberation unit as set forth in claim 4 wherein each of saidmagnetic members comprises a cylindrical permanent magnet having apredetermined diameter, the spacing between each damper and the adjacentmagnetic member being less than said predetermined diameter.

6. A reverberation unit as set forth in claim 3 wherein each of saidtransducer bases has a bore in which the respective damper is mounted,each said bore having a predetermined diameter, the spacing between eachdamper and the adjacent magnetic member being less than saidpredetermined bore diameter.

7. A reverberation unit as set forth in claim 3 wherein said torsionwire has a predetermined diameter, and wherein the spacing 'between eachdamper and the adjacent magnetic member is on the order of twice saidpredetermined diameter.

8. A reverberation unit as set forth in claim 3 wherein each of saiddampers is a cylindrical member having a predetermined diameter, andwherein the spacing from each damper to the adjacent magnetic member isless than said predetermined damper diameter.

9. A reverberation unit comprising a supporting base, a

pair of electromagnetic transducers mounted on said base in spaced apartrelation, and a helical spring stretched between said transducers, eachof said transducers including a base, anchor means on said transducerbases, a

torsion wire secured to one anchor means of each transducer Ibase andsecured at the other end to the adjacent end of said helical spring, amagnetic member on each torsion wire adjacent said spring and remotefrom the corresponding anchor means, and a cylindrical damper mounted oneach transducer base and having an axial hole through which thecorresponding torsion wire extends, each damper being cylindrical inconfiguration and having a greater axial length than the diameterthereof.

10. A reverberation unit as set forth in claim 9 wherein each damperfurther has a circumferential mounting flange thereon.

11. A reverberation unit as set forth in claim 10 wherein thecircumferential flange extends radially out from each damper and isdisposed relatively adjacent one end of the damper, said one end beingthe end remote from said spring.

References Cited UNITED STATES PATENTS 2,982,819 5/1961 Meinema et a1179-1.6 3,106,610 10/1963 Young 179--1.6 3,159,713 12/1964 Laube 1791.63,270,300 8/1966 Van Leer 333-30 R. P. TAYLOR, Assistant Examiner.

